hi again:waving:. i have 70 chevelle, 350, 280H comp cam, 67cc dart heads, rpm performer intake, msd 6al box, mallory vac advance hei distributer, etc...i submitted a topic a few weeks back about a bog i was having when i engaged the kickdown. i have a holley 750 vac sec and someone suggested going to a stiffer spring. made sense, so i bought a spring kit and went up one stiffer (purple), there was some improvement-but not enough, so i went up one more (brown), more improvement-but still a little bit of a flat spot. so i went to the stiffest spring (black) and now i feel the secondaries aren't even kicking in-major loss of power. so i guess i went to far and should go back down to the brown or purple. am i right so far? but if i do, what next with still having that "flat spot"? should i concentrate on jetting up? or down? (72 jets in primary now). is there something else i should be looking at? plugs look a combination of mostly tan, some of the insulators have a little black spot. i'm really stuck what to do next. help, please :confused: .

Well they say that you shouldn't feel the secondaries come in at all.

I can only suggest tuning the secondarie spring at the track.

If you are running pump gas you won't have too much to read.Look here
http://members.uia.net/pkelley2/sparkplugreading.html

Have you played with the advance curve and set the total advance?

have not played with advance curve. distributor has springs it came with, i did wonder if that came to play in this. i don't race at the track, not yet. i did read info on plugs, thanks, i think i'm burning too rich. should i try jetting down before moving on to anything else? i feel that is only some of the problem.

Rose, a couple of things. If you dont mind pulling the carb off, check and see if the secondary transfer slot ( a little rectangular cut in the carb bore ) is "peeking out from under the secodnary throttle plate. You should just, and I mean just be able to see it. Adjust the secondaries with the set screw to open or close more.

But before you get all into the carb, PLEASE set the timing. You really need to focus on total timing. Unplug the vaccum advance , if you have one. Rev the motore slowly to 3000 rpms+ with a light on and see where the timing goes.I would rev it to maybe 3500, or until you notice it stop advancing. You want this to be around 37-39, but it varies motor to motor. Some like more, some less. Turn the distributor until you;re there, say 38. Then let it go back to idle. Make a note of the inital timing now. If its running all crappy right now, don't fret, plug the vaccum advance back in. Make a mental note of where the timing is now. Then you'll have set the total advance and know exactly where to set the intial WITH VACCUM ON, to get to 38 total. Then you can start tuning the timing and see where your engine prefers it.

OK. Step two is adjust the float levels in that Holley before you do ANYTHING to the carb.

Lets see if that irons it out. Then go to step one above, and possible also jet down the primary side by 2 sizes while the carb is off.

Before proceding you need to set the total timing with a dial back timing light.

You need to do this first because there tons of people who blame the carbs poor performance on their carb when it is really the ignition not being set correctly that is causing the problem.

I now see you have a Mallory HEI.The advance curve in it shouldn't be too bad.

Plug the vacuume advance and rev the engine untill advance stops coming in.Make a note of this RPM.
Now rev the engine slightly higher than the predetermined RPM and set your total timing at 34-38 degrees.

Reconnect your vacuum advance to a ported vacuum source (sticking out of the meetering block) and test.

If it is the same reconnect the vacuume advance to the manifold vacuume source on the throttle plate (at the very bottom of the carb).
Now retest.

One of these vacuum connections will work better than the other,use the better one.

If the better performing one makes the engine ping with light to medium throttle applications you will need to get a vacuum can with slightly less advance.

After those basic settings is when you can start to play with your carbs accelerator pump and metering systems.

i appreciate all your suggestions. i just recently had someone install a different cam for me and i'm sure he did all that with the timing. he's very professional and he has his own business, maybe i should take it back out to him, i was just trying to do this on my own. i think i'm just making it worse graemlins/sad.gif . maybe i'll get a wild hair this weekend and try your suggestions. thanks again. smile.gif

Don't fret smile.gif
Many so called "Professionals" overlook setting the timing at full advance.
A performance engine should never have the timing set while idling.

Originally posted by thrasher:

A performance engine should never have the timing set while idling. Unless, of course, you know how much advance is in the distributor and even then a quick check of the total is a good idea.

i went thru the same ordeal with my 750 vac sec holley.

i tuned my secondary's to the race track and ended up with the tall yellow spring gave a 1.5 mph increase and droped my e.t almost .15 with back to back runs with a spring changed from the standard spring to tall yellow.

but on the streets specially for passing gear it would bog......you just felt the secondary's flop open it seemed like........but if you ran the car from a dead stop it was smooth and pulled hard.

so i put back in the stardard spring and this made it better. there was still something funky going on before thou. when i stepped into the gas and it would kick down for passing gear the car always had a slight flutter(hiccup). but i never messed with it.

but it started to bug me and i wanted to see what i could do to fix it.

i went thru the same thing i put the stiffer springs in the secondary's but it never got better. so i went back to my timming.

the first thing i did was i pulled the vacuum advance hose off completely. check my timming to make sure and it was at 20* initial and 36 total.

i took a test run with my normal regular secondary spring in it. and no vacuum advance hooked up. well there was no problem now.

so i then hooked up my vacuum can to full port like normal and took it back out. i did it. it had the same funky flutter.

back to the house i took off the vacuum line and went to ported. crap that made it worse. now i really had a funky flat spot.

so back to the house. i unhooked the vacuum canister again and started to map out my curve on paper reading my timming at given rpms. i notice i had a jump in my curve from about 1800 to 2800 rpms.

i changed one weight then one spring then i did a bunch of changes to the weights and springs to the point i lost count.

i finally ran across a combination that slowed my curve down. and it was much smoother.

with the same setting 20*/36* i hooked everything up and took it for a test run.

after a full day of messing with that darn thing it was gone. and now im running the tall yellow spring with out no hiccups.

so to me it was in the timming curve. some how the timming was flopping around when the passing gear was being kicked in.and the full vacuum port was some how was making this show up worse. i think the motor was being "shocked" with to much timming until the lighter springs got the weights under control.all i know the old curve with ported/or full vacuum was doing something funky.

i ended up with a heavier spring and a lighter weight in the combination.

now im not touching that hei. to me it is set.....lol

my timming is comming all in about 3000-3200 rpms just like before but it is slower. instead of just jumping up into it.

and that slower curve seemed to do the trick. i never figured out why ported or full vacuum made it worse before. but it runs great now with the slower curve.and with full vacuum to the can.

I ran into the same problem with the timing curve and vacume advance when tuning my last engine. I also ended up tailoring the mechanical curve to the engine and not using any vacume advance. I probably lost some fuel mileage not running the vacume advance but the engine pulls without hesitation under any driving conditions now. I do plan on experimenting with the vacume advance to see if I can apply somemore advance at part throttle cruize rpm.

ok. i took all yall's advice and tried a couple of things and it worked. (esp. moving the vac hose from distributor to carb to a different source, bottom of carb instead of top of carb-idles much better too). i still have some of this and that to try, but overall: she is running extremely better, much more responsive and far more quicker. i was amazed! it was all with jetting the carb down. i'll give it a week or two and check the plugs again and go from there. timing is right on. thanks.

graemlins/beers.gif I love it when a plan comes together.

I am glad that you had some sucess.

I am also glad that you reported back.I just hate it when people leave all those who gave advice hanging.
It puts a good end to a thread that someone might read from the search mode graemlins/thumbsup.gif

Glad to see you makin' some progress.Now that you have gotten this far, have you checked how much vaccuumm your carb's pulling at idle with the new settings?? And what power valve size is in the carb??

no, i haven't that yet, but i will. i came across another problem today. :confused: i seem to have created a hesitation in the carb at normal acceleration (it even gave me a couple of backfires-engine was cold.) i give it gas, it hesitates for about a second and then takes right off. i know this is not normal, especially if i get an occasional backfire. car is running so much better, this seems to be the only problem i have now. what did i do to cause this? here's a basic rundown of what i've done.
* went down on jets from 70 to 68.
* went one up stiffer on vac sec spring (but that was 2 weeks ago.)
* put new plugs in and gapped them at 50 instead of 45 like i had the other ones. (i did this because the instructions that came with my MSD 6al box said to try different variations until i get the best performance.)
* and double checked total timing. i had someone with a good timing light do that for me.
so what do i do now? help, please. i'm trying to not give up because i know i'm close.

Originally posted by ChvyRose:
no, i haven't that yet, but i will. i came across another problem today. :confused: i seem to have created a hesitation in the carb at normal acceleration (it even gave me a couple of backfires-engine was cold.) i give it gas, it hesitates for about a second and then takes right off. i know this is not normal, especially if i get an occasional backfire. car is running so much better, this seems to be the only problem i have now. what did i do to cause this? here's a basic rundown of what i've done.
* went down on jets from 70 to 68.
* went one up stiffer on vac sec spring (but that was 2 weeks ago.)
* put new plugs in and gapped them at 50 instead of 45 like i had the other ones. (i did this because the instructions that came with my MSD 6al box said to try different variations until i get the best performance.)
* and double checked total timing. i had someone with a good timing light do that for me.
so what do i do now? help, please. i'm trying to not give up because i know i'm close. You said in the first post you were running 72's in the primary. Which is it? If you did indeed have 72's, you just dropped 4 jet sizes. For all intents and purposes, jet changes should be done 2 sizes at a time. IF you hold steady on the gas at 45 MPH, is it surging at all? That would tell you the jets are too lean. Id stick 70's in the there and see what happens. IF youre timing is on, it has to be the carb. IF its only from a dead stop, go up one or two shooter sizes and see what happens.

i did originally drop from 72 to 70, then to 68. and gave it a week in between. plugs still read too rich. i'm gonna go ahead and take my gap down to 45. this is the only thing i can think of for now. i did notice one of my new plugs was the wrong one, a 576s and not 576, so i changed that but still have hesitation that i did not have before i gapped them to 50.

Originally posted by ChvyRose:
i did originally drop from 72 to 70, then to 68. and gave it a week in between. plugs still read too rich. i'm gonna go ahead and take my gap down to 45. this is the only thing i can think of for now. i did notice one of my new plugs was the wrong one, a 576s and not 576, so i changed that but still have hesitation that i did not have before i gapped them to 50. How many turns out are your idle mixture screws at? That could be fouling the plugs out. Were they set with a vacuum guage? If not, try it- set for highest vacuum. Then take the reading that you get after tuning the screws as best you can, and make sure the power valve is below that HG point. I doubt that plug gap is the problem if it is only doing it at a certain speed. If the plugs were that far off, it'd run like crap all the time..

wow, thanks, it's funny, but a friend of mine was just suggesting that. so, what you're saying is that the hesitation i'm getting is due to jetting down too much because my plugs may be too rich due to improper idle adjustment?

Originally posted by ChvyRose:
wow, thanks, it's funny, but a friend of mine was just suggesting that. so, what you're saying is that the hesitation i'm getting is due to jetting down too much because my plugs may be too rich due to improper idle adjustment? No, actually what Im thinking is that a RICH IDLE could be fouling out your plugs, and you might be THINKING its the jets, and making too large a change for tuning purposes. In my Holley book, that carb came with 72's. Probably OK, but maybe a tad on the rich side- which wont be PIG rich, though. No decrease in size for your altitude, so its really just "tuning".

Like I said earlier, does it surge any at a steady 40-50 MPH cruise speed? You are completely out the idle circuit at that point, and the secondaries arent a factor either.

If it was me, I would adjust the mixture screws FIRST for best vaccum. Check and see, when you adjust the mixture screws, where your HG is at then pick the right Power Valve. Id bet the stock one is OK though. Anyway, AFTER you have the mixture screws set, and you KNOW that the idle is "clean", THEN rejet if you want. But I personally would only drop to the '70s if it was me- at least initially. Normally, you drop until there is a lean out, then go back up two sizes; ie. start at 72- go to 70, it leans out at 68, back up to the '70s.

If it STILL wants to act like its not getting gas from a stop, get a few shooters- maybe a .026, and .027 or whatever is closest. I see it came with a .025. Sometimes too small a shooter causes what you are describing.

Do yourself a favor, and count the turns OUT that the screws are NOW before making ANY changes to them. That way, if it IS the jets, you can easily put the mix screws right back where they were. Same goes for giving yourself a "rich idle" baseline too, I suppose.

Bottom line, only make a few changes at a time- or it will just seem like its spiraling out of control. Actually, ONE change at a time is best..

thanks once again. i will let ya'll know. ;)

Take the advice...

Only one change at a time.If it doesn't make it any better,put it back how it was.
Then make another change and see what that does.

If your plugs were badly fouled they will not clean up well and should be replaced.Some of my friends have tried to tune on plugs that have bean fouled before.It just doesn't work.

hey, graemlins/waving.gif just wanted to let you know i tuned the carb like you said. highest vacuum reading was at 1 turn out, which was actually only 1/4 turn off from where i had it, at 3/4 out. i get confused :confused: about which way to turn it but i figure turning screws out gives you richer mixture and turning screws in gives you leaner mixture. am i right? so, if anything, i've only made it richer, graemlins/sad.gif . but i did notice one thing, i may have misread the reading on my gauge from before when choosing my power valve so i'll head back to the speed shop and show them where it reads on my gauge to guarantee i get the correct one. i'll check the plugs in a few days and let ya'll know what's up. talk to ya in few. thanks. smile.gif

what did you do with your timming? what is the intial timming and total timming? and when is your total timming comming in at? then what is your timming with the vacuum canister hooked up to full port read?

from what i read on your engine specs your initial timming should be around 16 degrees at idle. with no vacuum advance hooked up. and you should have around 36 degrees total all in by 3000 rpms.

with this set up you should have a vacuum canister that gives no more then 20 degrees extra when hooked to full port. your engine would be happier with a with anything under 20 degrees vacuum can........the vacuum canister gives you extra timming at idle and at cruise speeds to help burn your fuel more effeciently. and provides for a smoother idle and better gas mileage.

but you have to be careful not to give it to much timming other wise you may run into a highspeed miss. because there is to much timming.

if you have a canister that provides 20 degrees extra in timming the you will see 36 degrees at idle and 56 degrees at cruising rpm provided your tunning about 3000 rpms down the road say at 70 mph. and your timming will be seen this way by the motor when it is hooked up to full port vacuum like you said you changed it too.

the timming has to be set and dialed in before you can move on to the other tunning aspects of the carb. this is a must!

once you have the timming issues dialed in and set now it is time to set the floats on the carb. they must be set to were they just trinkle out the site holes when you bump the car.

now it is time to set the idle mixture screws.

with a vacuum gauge in hand. hook up the gauge to full port vacuum off the carb base. let the motor warm up to full temp. have a helper put the car in gear. and set your idle to the lowest possable rpm with out stall.and make sure you have your air cleaner assy on. now you can turn in or out your mixture screws to the highest vacuum reading.

once this is done make note of the vacuum reading and make sure your power valve is at least 1.5" below your vacuum reading. if it is 12" of vacuum you can run a power valve as high as 10.5 but you have to remember anytime you hit the gas even under light throttle the vacuum can drop below 10.5" and your carb will send extra fuel to the motor when it may not need it.......so it would be fine to go to a 8.5 even.

now you can adjust your idle to your likings.

it is very important that you set your idle mixture screws with your air cleaner on and in gear.and engine warmed up to temp. at this point you idle circut is all taken care of.

(now with your carb the stock 72 jets are just fine for a starting point they should be the last thing you do to the carb.)

after you have your idle set were you like it, it is time to move onto primary side of the of the carb. we are looking at anything from idle to half throttle. specially the squiter. you should be able to move the throttle from idle to half throttle with out any hesitation. look for loose squiter arm......it should react with just the smallest amount of throttle movement. if you have any hessitation this needs to be addressed. with in most cases a larger squiter shot. going from a #25 to #28 or changing out the squiter pump cam.

once this side of the primarys are taken car of it's time to move onto the secondary side with making the right selction of the vacuum spring. this you have to test drive. when throttle is mashed to the floor it should be smooth. if you have a hessitation your secondary spring is to soft and the secondarys are flopping open. use the spring that gives you the smoothest transfer you shouldnt "feel" them kick in.

now you are ready to adjust the primary jets. and this can be done looking at the plugs after a full rpm run. its not a good idea to cut the motor clean say at 6000 rpms with an automatic. just make a hard run and slow down as fast as you can and turn the motor off. check the plug and see what they look like.

being that your car has a metering plate in the rear there not alot you can do for that unless you convert to block or buy different plates........so otherwise you have to jet up or down on the primary side to make sure your not running lean on the top end.....

i know this is alot to take in and i hope i didnt miss to much.......it is way easier for me just to tune a car then it is to try and tell all the step involved.

ok, so i haven't done all that everyone has advised me to do. but i'm taking baby steps here. the way i see it, i made a couple of changes that made several things better and created one problem. so i'm going to get thru my baby steps before i move on to the big picture. but i do truly appreciate all you guys have taught me. tongue.gif here's my update: i recalibrated the carb, was only 1/4 turn difference. hesitation still there on initial acceleration. so i regapped plugs back .45. still same problem. jetted back up to 70-hesitation went away! but doesn't run as good as the 68's. so, i regapped to .50, no hesitation (eliminated that as the problem.) now, tonight i checked plugs, looks just a tad bit rich on top wall, heat range looks perfect. so i jetted back down to 68. ran better again, but feel that hesitation coming back on initial acceleration. recalibrated carb again, with breather on and in gear, it's now at 1 turn out. will drive a few days to see. i might add, i no longer have bog in passing gear graemlins/hurray.gif , smooth, so i feel i have the correct vac sec spring (1 up stiffer). now, one of you guys mention squirter. could that be my hesitation. tell me more.

No problem. You put the 68s in and now you have that little 'hole' that opens up on acceleration. Two ways to cure this. 1.) put in a higher rated power vavle ( any idea whats in there now?), and/or 2.) increase the squirter size. The squirter is the small 'barrel' in the primary bore, held down by a phillips head screw.

The squirter hole size sets the rate at which fuel flows from the accelerator pump. A bigger squirter will flow more fuel, bringing it in quicker. Sounds like jumping up 2 sizes should do it. When you remove your squirter, you'll see the size stamped on it. That's what I would do next.

Actually, I'd also lessen the gap between the accelerator pump arms and see if it helps. You either expand or compress that "coil-over" bolt that pushes down on the pump arm. By opening the gap ( compressing it) , you have less volume and there is a slight delay. By closing the gap( expanding the bolt) , the shot somes in faster.

cool. :cool: thanks for the quick response. i will check my power valve first, then, if necessary, address the squirter. graemlins/thumbsup.gif
p.s. don't i know you? i think we use to chat way back.

Heck, Holley jets are so cheap go buy some 69's and see what happens. If anything, you'll be on your way to a nice collection of tuning stuff. If 70 is a tad rich, and 68 is a tad lean, 69 should be ideal. I mean were talking a range of 3 jets here, not 10 jets. 70 was to get it back to a baseline. As I said, it came with 72's. Before I went out and bought a squirter (1 is about the cost of 2 or 3 jets), Id take the $5.00 and get a set of 69 jets and put them in- Id bet that they would work great. If it still had a hesitation, THEN Id go ahead and get a little bit bigger squirter for your car. It actually is a little better to try to get rid of hesistations and stuff with jets/power valves FIRST, and then start tuning with squirters and the like for maximum power/best tune.

I hate to sound like a broken record, but IF you are having a surge at a steady speed 45-50MPH cruise, the jets are too lean and they just arent the "best" ones. Its an easy way to "test", but you havent really mentioned anything about it. IN any case, Id still try the 69's.

Also before doing anything else, follow 427L88's advice and make sure the pump arm is just where it should be.

buzzbomb, i haven't noticed a surge, it seems to be pretty consistently smooth at that point out. but maybe i need to pay more attention to that to make sure it's not happening and i'm missing it. thanks.

(1) Check your vacuum at an idle in gear.
What ever the reading is reduce this reading by 1-1.5 and install that number powervalve.

Example;
If your vacuum reading is say, 8inches,
go to the local hot rod shop and get a 6.5 valve and install.


(2) The following is best done with the help of one of your friends smile.gif

Set your accelerator pump arm clearance.
Give it wide open throttle and hold it there.
Now gently push the diaphram lever down untill it stops moving.
Now take the accelerator pump arm (the thing with the bolt,spring,and lock nut)and gently raise it up untill it stops moving.

Now take a .020 feeler gauge and slip it between the two while you have the lever down and the arm lifted.

If it is hard to get the feeler gauge between the two you need to create a greater clearance between the two.
If the feeler gauge slips in there easily and has no slight drag when withdrawn you need to reduce the clearance.

To adjust the clearance put a wrench on the bolt that is attached to the accelerator pump lever.Now put a wrench on the nut.
Turn the nut counterclockwise to reduce the gap(lengthen the spring)and turn the nut clockwise to increase the gap(compress the spring).

Now that this adjustment is done make sure you have no clearance between the pump cam(the plastic thing) and the pump arm at an idle.
If there is clearance slightly turn the accelerator pump nut counterclockwise a little untill it is gone.

Now give it full throttle again and then press down on the accelerator pump lever to see if it moves.If it moves a little you are good to go.
If not further adjustment is needed.

It's easier to do than to explain ;)

Do not work the throttle too much when setting the accelerator pump arm clearance as you will regret it :eek:

427l88: i read over your response and missed the last paragragh the first time, i must have been dr--k at the time redface.gif , but i had thought about adjusting the accel pump arm, but was not sure which way to turn it. she's definately running much better, so i feel the jetting down to the 68's was the right move. i haven't done anything more since last weekend. going to check plugs this weekend. thanks again. things are looking up. graemlins/thumbsup.gif

thanks thrasher, i'll be back next week to let ya'll know what happens. your right, it's always a good idea to let everyone know the results, so others will learn from it. talk at ya'll in a few. smile.gif

buzzbomb, i've been reading over everything again. haven't checked plugs yet, that'll be tomorrow night. but, you may be right, it hesitates and then surges, at about that speed. i guess that is the best way to describe it. so, before i do anything else, i'm going to pull plugs, then try out 69's. the plugs should tell me alot, i put in new ones right before i jetted down to 70's, which was only two weeks ago, and i jetted down to the 68's a week later. so, that's my next move. i'll be back...

Originally posted by ChvyRose:
it hesitates and then surges, at about that speed. i guess that is the best way to describe it. IF the car is surging (feels like its not getting enough gas, then it is, then its not, etc) at a steady 45-50 speed, IMHO, its jetted to lean. Like I posted- put some 69's in there and Id bet it all comes together, providing of course that all the other stuff is right.

If it surges at constant throttle and hesitates at those speeds you are more than one jet size off.

I am going to say this again:
Check Your Vacuum reading At An Idle In Gear and Get the Appropriate Powervalve.
The powervalve effects the fuel curve while driving.

Did you already do this or did I just miss you stating that you did?

What type of air cleaner assembly are you running and how tall is the filter?

The reason I ask is that if the filter top is too close to the bowl vents it will cause metering problems.Not saying that is what it is,just want to know to eliminate that as being a problem.

thrasher, yea, i mean that was already my plan about the powervalve. i do have an accurate vacuum reading, did it just like you said. i'll take my guage to the speed shop today and show them what the reading is, and install the right one, don't remember what's in there now. the air cleaner is an aftermarket, about 10 inches in diameter, with a K&N filter, i think it's about 3 inches tall.

" have 70 chevelle, 350, 280H comp cam, 67cc dart heads, rpm performer intake, msd 6al box, mallory vac advance hei distributer, holley 750 vac "

First off, I doubt you are idling with anything LESS than 12-15 inches of vacuum. A vacuum gauge is SUPER easy to read! Whats it say? The speed shop can only do so much :confused: - thats how YOU learn.

Secondly, the power valve is NOT really a metering "circuit". Of course, it IS, but its one of those things that is more or less "on demand"- unlike the jets. Think of it as a gas switch- when your vacuum drops, the power valve switches on. If you get a 10.5 power valve, that would mean that it would come on MUCH earlier than it should, causing a too rich condition. I would bet you are running a 8.5 or 6.5 valve- which is fine for most applications. 8.5 might even cost you mileage. IMHO, surging at a steady speed is JETTING not power valves. IF it was leaning out after nailing it, yea, Id look at the pvalve. BUt a power valve is not a cure all for lean jetting. You already tried 70's, they were "rich" (only going by what you said- Its all we can go on), and 68's are causing surging at a steady cruise- LEAN. In reality, a Holley 70 is a .069, and a 68 jet is a .067. Holleys are fat out of the box, but usually need to be dialed in only within a few numbers.

A squirter causes NOTHING at 45-50MPH- so leave it alone.

Thrasher makes a good point about the air cleaner top. Make sure the vent tubes have enough clearance- otherwise you will get the symptoms you are talking about- and will chase it forever.

ok. let me make sure i didn't explain my symptom wrong. i only feel this "hesitation and surge" after acceleration, not while keeping the same speed. also, don't think breather is a problem, made no difference running without one, which i tried for a couple of days.

i just pulled out four of my plugs. this is what they look like: the base ring, which determines jetting and air/fuel mixture, right? has a 3/4 to 7/8 turn layer of black. still too rich, right? shouldn't it be more of gray layer of color? according to the "plug reading" article one of ya'll sent me a 3/4 to 7/8 turn indicates on the ragged edge of being lean, but the color i'm getting indicates rich. :confused: my air/mixture screws are only 3/4 a turn out, if i turn them "in" any more the engine wants to die.

also my vacuum reading is 10 inches in gear. at idle it's 2 more marks up (no numbers above these marks so i'm guessing 12 or 13). that's with breather on.

"i only feel this "hesitation and surge" after acceleration, not while keeping the same speed."

Try a new squirter. You have to be specific. Since you are describing something totally different, It may NOT be jetting now. STEADY STATE is holding it at 50mPH and leaving it there.

"don't think breather is a problem, made no difference running without one, which i tried for a couple of days."

Well, at least youve eliminated that.

IF youre looking at the plug reading thing I think youre looking at, that is ONLY for reading plugs when you cut if off after a full throttle run. IT specifically states that in teh article. IF not, well...I like NGK or the GN site for plug condition. Rich conditions are obvious in any case- if the whole plug is black, its pig rich.

"if i turn them "in" any more the engine wants to die."

Thats good. Thats the lean drop off point. Youve eliminated mixure as a possibility for the most part.

"also my vacuum reading is 10 inches in gear. at idle it's 2 more marks up (no numbers above these marks so i'm guessing 12 or 13). that's with breather on."

SOunds reasonable to me. Thats why a 8.5 or maybe 6.5 PV is just fine. Thats why Holley puts those PV's in 95% of their carbs.

Since you recanted what you said about the steady state speed, and state now that its only from a stop- try a bigger squirter...Couldnt hurt to make sure your fuel filter is clean.

i like the way you respond to each question, makes it easier to decipher. smile.gif one more thing i want to clarify and you tell me if you have any different thoughts...when i mean hesitation and surge on acceleration, i don't mean just from a dead stop, i also mean when i get up to a certain speed and want to go faster and nail it a little that's also when i feel it. so, same thing, right?

p.s. i think i have a 6.5 pv in now, i picked up a 8.5 today. will also check out the site about plugs.

Originally posted by Buzzbomb:
Secondly, the power valve is NOT really a metering "circuit". Of course, it IS, but its one of those things that is more or less "on demand"- unlike the jets. Think of it as a gas switch- when your vacuum drops, the power valve switches on.

True.

IMHO, surging at a steady speed is JETTING not power valves. Surging can be caused by the powervalve.

If you are crusing (constant throttle)at the powervalve opening inch point and your jetting is lean you will feel the engine surge as the powervalve fluctuates back and forth between open and closed.

This is something I have experianced first hand when experiamenting with jets and powervalves with my old 650DP on my daily driver.

It is a switch.
NASCAR tuners use it to save gas during caution flags.Cruseing below the powervalves opening point causes the carb to be leaner,thereby saving fuel.

Originally posted by thrasher:
Surging can be caused by the powervalve.Yea, but the window is pretty narrow. Say its a 6.5 valve- after vacuum drops below that, its all the same valve. I might be wrong, but steady cruising is not a heavy or moderate load condition, hence there is much more than 6.5 vacuum (his valve). POwer valves are usually for hitting the gas, not holding it steady. He does have a cam in there, but I really doubt he cruises at 6.5 hg- who knows? MIght be a good idea to check it.

I would bet those Nascar engines make a lot less vacuum than his car does. SO, I still believe its the jets. Im saying that in respect to tuning the car. IF all he wants is to cover the stumble hole earlier or artificially, by all means get a 10.5 power valve.

Its certainly no big loss to have a few of the most commonly used jets and powervalves graemlins/thumbsup.gif

hello, me again, fyi-i'm a girl. can't you tell by how amateur? redface.gif but anyway, i think first i will try out my new powervalve, it's a 7.5 or 8.5, then next i will try the 69 jets. if neither of those work i will try the adjust with the accel pump before moving on to squirters. i'm real close, guys, real close. be back soon. ;)

Originally posted by ChvyRose:
hello, me again, fyi-i'm a girl. can't you tell by how amateur? redface.gif You dont say? I thought maybe you just picked a flowery nickname for your car tongue.gif smile.gif

Originally posted by ChvyRose:
i think first i will try out my new powervalve, it's a 7.5 or 8.5, then next i will try the 69 jets. if neither of those work i will try the adjust with the accel pump before moving on to squirters. Sounds like a good plan. Id do the jets first- but thats just me. IN either case, you seem to understand teh most imporant concept of all this- DONT CHANGE A LOT AT THE SAME TIME! Pretty good- for a gurl... smile.gif . Im sure youll get it- just keep at it.

thanks. i do appreciate that. ;)

Originally posted by ChvyRose:
hello, me again, fyi-i'm a girl. can't you tell by how amateur? Well... It was either that or you were one of thOSE types :D

Man,after reading all of these posts,I'm sure glad I have Edelbrocks on my cars.Never had any luck with them there HOlley's tongue.gif
Good luck.
graemlins/waving.gif
Rick

Originally posted by Buzzbomb:
Pretty good- for a gurl... smile.gif . Im sure youll get it- just keep at it. /QUOTE]

:eek: I'm not going there!

That can be taken the wrong way ;)

No to be confused with the old;

Honey does this dress make me look fat :eek:

RUN RUN FOR YOUR LIFE!!!! tongue.gif

Too bad you don't live over here in Cali Chvyrose, help me fix my carb problems. Sounds like I'm kinda having similar problems with my carb, but I know mine needs a rebuild, it's in real bad condition. Good luck with your tuning, and I look forward to every post, hopfully something here will help my carb out graemlins/thumbsup.gif

true...it's tough being a girl in this sport. and i do get alot of the "isn't this your boyfriend's car :rolleyes: -oh boy here we go again." but the look on their face when i say "hell no, she's all mine. :D " i don't take it personal. the fact is most girls aren't really mechanical, but i also believe because they don't have an interest in it, so they're never taught. it's been hard the last ten years having this car and trying to get it where it is (needless to say i can't keep a nice set of nails). i've been ripped off plenty and learned alot of hard lessons. but the most important thing is: i got what i want graemlins/thumbsup.gif and i learned ALOT! (might i add i'm not gay smile.gif ). well, enough of that...i'll talk at ya'll later. smile.gif

Originally posted by ChvyRose:
might i add i'm not gay smile.gif That's good to hear, seems like the stereotype of woman who are into anything "guyish" are les. Keep up the good work and let us know how things are coming along with your car graemlins/waving.gif

Originally posted by 427L88:

Actually, I'd also lessen the gap between the accelerator pump arms and see if it helps. You either expand or compress that "coil-over" bolt that pushes down on the pump arm. By opening the gap ( compressing it) , you have less volume and there is a slight delay. By closing the gap( expanding the bolt) , the shot somes in faster. If you haven't tried this yet, I think you should. Expanding the bolt and thus closing that gap was all it took to cure my stumble. It won't cost a penny to try it and won't take more than a few minutes. Worth a try.

hello graemlins/waving.gif been too busy to work on her til tonight. i tried the adjustment with the accel pump arm-i compressed 1 full turn but it made no difference. pulled a couple of plugs again-i feel she's borderline lean. i think i'm gonna go ahead and try the 69 jets. let you know what happens. smile.gif

hey, depends on the setup, but I've always made great power on the lean side...

Now I wish I could lose some weight! smile.gif

Yeah, re Edelbrocks, sure they're better out-of-the-box, but if you want pure rip, Holleys can't be beat.

If you find the accel pump works best with there being no gap in the actuating arm, then you should jump up a squirter size.

If you don't have a little gap, you risk bottoming out the pump diaphram.

I think he means at wide open throttle.

Originally posted by ChvyRose:
hello graemlins/waving.gif been too busy to work on her til tonight. i tried the adjustment with the accel pump arm-i compressed 1 full turn but it made no difference. pulled a couple of plugs again-i feel she's borderline lean. i think i'm gonna go ahead and try the 69 jets. let you know what happens. smile.gif I'll tell you what...You are a woman, and out there ripping out plugs, changing jets..THAT is pretty cool, IMHO. Not keying in on that, but it is rather "different"- not bad "different" but good "different".

Anyway,

Its not a big deal to have 68-72 range of jets. You'll be able to rejet for altitude, track conditions, or whatever if need be without spending a bunch on needless jet sizes. I would still bet that it will help. What do your plugs look like? Are they cocoa brown/orangey looking or black, or are they gray? If they are in that range (other than black, of course), youre really close. All you are doing now is fine tuning.

After you replace the jets, and if by chance it DOESNT cure the stumble, THEN Try a new squirter ONLY after making the proper adjustment on the override spring.

And yes, it is done at Wide Open Throttle (car off of course tongue.gif ). Shove the throttle wide open, and see "if there is .015 to .020 clearance before the pump housing lever bottoms the pump diaphragm"..

"" from Dave Emanuels book.

Uh, no I meant "at rest". Yes, the real adjustment is done at WOT, but for tuning purposes ON THE PRIMARY side, I vary the gap " at rest" and take the car out to see how it responded. Its a tuning aid.

right, tighten the gap and the pump shot comes in sooner, open the gap it comes in later.

just dont get carried away, you can ruin the diaphram if you dont have enough clearance.

hey ya'll. graemlins/waving.gif it's been awhile. like i said, i did make an adjustment to the accel pump, but there was no difference. i put the 69 jets in, not much difference in performance, but it still runs more responsive than 70's. pulled plugs tonight, still too black as far as color, but only a 3/4 layer on top of plug. i'm going to address timing again. i really don't see how going to an 8.5 power valve from a 6.5 is going to help, plugs will only be more black. i got a feeling i need to invest in a more compatible carb. sometimes you can modify something all you want, if it's too much, it's too much. ya'll can see what i have in this thing, (go to first page)do you feel it's too much carb?

Have you tried changing to a hotter plug?

A vacuum secondary carb can really never be too much...It only uses what it needs. A 750 should be ok on your car.

Is the choke wide open when its all warmed up?

Did you do the right adjustment to the pump? Is it even hesitating like it was?

What vacuum is it at idle? Has it backfired with that power valve in there? If not,leave the power valve alone.

What initial timing are you running at? Are you using the recommended plugs for those heads?

hey again, graemlins/waving.gif haven't dropped off the face of the earth, just been too busy. had another problem come up that took precidence (is that a word? :confused: ) over anything else. fuel pump went out. it's an electric Carter mounted back by the tank, replaced it this weekend. was a bit challenging, never did it before, boy, it's easy to strip out brass fittings! and yes, i replaced all my fuel lines too. also, developed a vacuum leak at carb, had to fix with heli-coil-carb to intake manifold-it stripped out on me. one thing i noticed when i had carb off, i have a dual plane rpm performer, but my gaskets are completely open in the middle, is this a big deal?

well, it seems i'm starting from somewhat at square one. since i replaced the fuel pump and the stripped out bolt on carb things seem to be different. first: no longer have hesitation i had before, vacuum reading is still not where it was before, and seem to have a little loss of power, not running as responsive. i pulled a plug, which i put a new set in just a week ago, seems to be way lean as far as jets. so i put the 70's back in. initial timing is at 12. i really don't thing that is an issue. if i have a vacuum leak at another point, it doesn't seem to be at carb, i can't find it. i'll see what happens from here and let you know.

I DID IT!! graemlins/beers.gif as you well know, i ended up finding a vacuum leak at carb, had to heli-coil a bolt hole on intake, replaced carb gaskets, and, oddly enough, was able to lean it out another 1/4 turn without it dropping off. it doesn't want to idle good when you first start up but after only a minute, she's just fine and has a nice healthy sound. plugs are looking much better. also, went back up to 71 jets, anything less appeared to lean on the plug. pulled a plug again tonight, looks just about right. no hesitation and runs great!! it took awhile, i know, but i think the vac leak at carb that went undetected might have been part of the problem. now that i can lean it in a little more, that seems to make all the difference. very happy! ;) thanks for all your help. graemlins/thumbsup.gif
talk to ya'll later... graemlins/waving.gif

If you're available, you wanna work on my car? tongue.gif I've got a lot of tunning issues I need worked out with my carb. That's great to hear all your hard work has finally paid off. Now if I can only find the time and money to rebuild my carb and tune it up like you did :confused:

I read all of the posts on this thread, and all of you folks missed one thing (I think). I seem to remember reading that in addition to adjusting the accelerator pump arm, you can also change the accelerator pump cam position as well as changing the cam for a different one. The problem Rose was describing (the 45 to 50 MPH steady speed then accelerate and have stumble then surge) sounded just like one I was having on a 73 El Camino with a 350. Accelerator pump is designed to feed extra fuel when you open throttle blades more. Without the extra fuel you experience a momentary bog due to not enough fuel to go with all of the additional air you just introduced (that translates to a lowering of vacuum and less ability to suck fuel in, so you have to shoot more). By changing the accelerator pump cam action, you shoot the fuel quicker, matching the increased air and keeping the A/F ratio where it needs to be. It could also work the other way as well, shooting too much extra fuel too fast. I changed my cam position and completely eliminated my problem. Also, someone mentioned that you should not feel it when the secondaries kick in on a Vac secondary car. Everything I have ever read states the same thing. If all is running right, you should have a smooth power increase and not a sudden jump.